Various methods and devices are known for production of hydrocarbons from wells. One such method is a natural flow method of production of hydrocarbons from wells according to which a formation fluid flows from the bottomhole to the wellhead of a well due to oil formation pressure and energy of gas dissolved in oil. In course of operating the well using said method, formation pressure drops until it is insufficient for lifting oil to the wellhead, and the well stops operating. In that case a common mechanical method of oil production is used, for example, a gas-lift method. Maximum flow rates lead to a decrease in bottomhole pressure. However, the decrease in bottomhole pressure below saturation pressure results in oil degassing in the near-bottomhole zone of the formation, clogging of porous space of the reservoir by gas, and, consequently, in a decrease in oil production. To prevent this effect, at the wellhead is generated counter-pressure by means of a choke with its inner diameter selected so as to provide required bottomhole pressure, which may result in a certain limitation of oil flow rate. However, such maintenance of bottomhole pressure at a level not lower than saturation pressure, performed from the site of the wellhead, also may stop the flow regime of the well and cause the necessity to use a gas-lift or pumping method of oil production.
According to the gas-lift method of oil production, a compressed gas is injected at a certain depth into the production tubing to aerate the formation fluid in the tubing upon a decrease in well pressure due to lifting of the flow, hereby reducing the fluid's weight, so that the aerated fluid flows up towards the wellhead, and the bottomhole pressure reduces. At the same time, the difference between the formation pressure and the bottomhole pressure increases and oil starts to flow from the formation through the well from its bottomhole to the wellhead. The main disadvantage of this method is high production costs due to increased oil well operating expenses, including expenses for gas, compressor equipment, pumping energy, control systems. Besides, efficiency of the gas-lift method is relatively low.
Another method of oil production is disclosed in a U.S. Pat. No. 5,105,889. According to this method of oil production from wells with a reduced formation pressure, gas dissolved in oil is forcedly liberated from the oil flow at the bottomhole part of a well, and the oil flow is hereby transformed into a finely-dispersed gas-liquid flow so, that the pressure of gas-liquid column from the site of the transformation to the wellhead, in sum with the wellhead pressure, less friction losses, becomes lower than the saturation pressure and lower than the difference between the bottomhole pressure and the pressure of the fluid column from the depth of the formation occurrence to the location of said transformation. In case of such oil transformation in a well, oil lifting to the wellhead occurs due to energy of gas dissolved in oil, without any additional energy sources, even in wells with a reduced formation pressure. According to this method, to prevent oil degassing in the bottomhole zone of the well and consequent decrease of oil production, the bottomhole pressure is established and maintained to be higher than the saturation pressure by means of throttling; at the same time, the inner cross section of the flow channel is reduced and flow speed consequently increased to reduce the flow pressure below the saturation pressure, hereby forcing degassing in the whole fluid column of the well. A device for performing this method consists of a body with a nozzle installed in the body and aligned with the well, which body is fixed hermetically in a compressor tube, and Venturi tubes installed in the body above the nozzle and aligned with it, for forced liberation of a gas dissolved in the formation fluid and transformation of the flow coming out of the nozzle into a finely dispersed gas-liquid flow. In this device said venturi tubes are installed in the upward sequence and aligned.
The above method is more advanced than gas-lift, since it provides creation in a well of a gas-liquid flow of lower density; stabilization of bottomhole pressure, preventing of oil degassing in the formation and at the well bottomhole; maintenance of the wellhead pressure at a level providing gas-liquid flow to the wellhead and preventing its phase separation, to hereby prolong or restore flowing regime of the well without any additional energy sources, to reduce operational costs, and to increase efficiency of oil production in general.
During the process of oil production various hydrodynamic and gas dynamic changes occur which influence the work of producing wells, such as a drop in the formation pressure due to oil intake from a reservoir, which results in a reduction of well flow rates; a drop in the formation pressure due to interference to changes occurring in adjoining wells, such as stoppage of a well for repair, introduction of a new well, etc. which also results in a reduction of oil production; a reduction of gas content in the oil, an increase of water content in the production; a depletion of separate formation layers, which also leads to a decrease in well flow rates; junction of cracks together in porous reservoirs in the bottomhole zone of the formation; an increase in the formation pressure due to pumping of water down injection wells, etc. All said natural and technogenic processes occur at deposits all the time and affect well operation to some or the other degree. If said changes, occurring irregularly at different deposits and wells, are not taken in consideration, it may lead to a drop in the formation pressure, a decrease in the formation pressure gradient; a drop in the bottomhole pressure below the saturation pressure, a water/oil ratio increase, a change in the gas content and the saturation pressure, which consequently may result in a reduction of well flow rate, an expeditious gas break through wellbore flow, an unstable working regime of the wells, even the production shutdown of the wells. In the event of the above, it will be necessary to use more expensive and less efficient secondary mechanical methods of oil production.
According to the method disclosed in the described above U.S. patent, it is possible to partially control said processes by means of a bottomhole and a wellhead facilities: a wellhead valve which automatically regulates the proportion of gas-liquid mixture from the site of its origination in the well to the wellhead, preventing creation of an annular mist flow regime, and the bottomhole device which permits correction of the well operation if any changes occur, by means of periodical replacement of Venturi tubes in the device with the new ones with different parameters in correspondence with any changes in properties of the formation and the formation fluid, for example, changes in bottomhole pressure, gas and water content in the flow, well flow rate, and so on. Operation of a well stops during such replacements, additional expenses on the replaced equipment occur, well operation becomes more complicated and less efficient due to step-by-step change of the device parameters.